The goal of this project is to develop and test probes of the apelin (APJ) receptor for in vivo studies related to preeclampsia (PE). Preeclampsia is a complex maternal hypertensive disorder noted in ~7-10% of all pregnancies and accounts for ~100,000 maternal deaths globally each year. Current therapies are inadequate. Preeclampsia is linked to hypertension and inflammation, coupled with impaired vascular endothelial function due to inadequate placentation, and impaired utero-placental perfusion. This results in hypoxia and altered angiogenic balance within the developing fetus. The G-protein coupled receptor (GPCR) protein APJ may play a regulatory role in PE. APJ is activated by circulating but metabolically labile apelin peptides in vivo. APJ is expressed within the vasculature of most organs including placenta. Activation of APJ promotes vasodilation and angiogenesis. Interestingly, APJ knockout (ko) mice suffer from heart failure, demonstrate reduced angiogenic potential, and have reproductive deficiencies (reduced number of pups). Apelin also induces formation of large blood vessels during functional recovery from ischemia, which is a hypoxic and vaso- occlusive disorder like PE. Our published follow-up studies in human patients indicate that the odds of PE are 48% lower for women with high versus low plasma apelin concentration. Past studies also indicate that local apelin and APJ are up-regulated within the placentas of human PE patients perhaps as a compensatory mechanism. Thus, the apelinergic system should be investigated both mechanistically and pharmacologically within the context of PE. However, in vivo studies of APJ are difficult at the moment due to a paucity of available drug-like small molecule ligands of this receptor. To date, our group has made significant progress in this regard. We have developed appropriate assays for APJ and completed a screening campaign to identify hits. These compounds have been refined to produce full-agonist of APJ that are potent (EC50~100 nM). We propose to further refine the drug-like properties of these compounds using iterative synthesis, evaluation, and optimization of drug-like properties using a battery of in vitro assays. Select compounds will undergo pharmacokinetic (PK) testing to identify candidate probes for in vivo testing. We hypothesize that optimized probes of the APJ receptor will produce beneficial anti-hypertensive and pro-angiogenic effects while reducing oxidative stress in preclinical models of PE. Thus, compounds will be evaluated in a well-validated, surgically altered reduced uterine perfusion pressure (RUPP) model of preeclampsia in Sprague Dawley (SD) rats that reproduces several symptoms of the human disease. Blood pressure, angiogenic balance, and oxidative stress related biomarkers will be evaluated. Further, reproductive toxicological analyses will be performed to rule out adverse effects. Successful completion of this project will lead to new in vivo probes of APJ that will enable further studies of this receptor within the context of health and disease.